W11: Invertebrate Physiology (Insects & Elevated CO2) [Dr. Blair] Flashcards
Insects & Elevated CO2?
As CO2 levels increase from 300ppm to 420ppm, there have been physiological implications for all life on Earth.
Direct effects of elevated CO2 on insects? (3)
- Mostly minimal.
- No respiratory implications.
- To succumb to toxic effects, CO2 levels would have to reach ~40 000ppm.
Indirect effects of elevated CO2 for insects? (5)
- Major concern, as it’s causing,
- High mortality.
- Decreased reproduction.
- Decreased development.
- Decreased survival.
What kind of insects do elevated CO2 greatly affect?
Phytophagous insects.
Phytophagous insect attributes? (2)
- Major group of more than 500 000 species.
- All plants have at least 1 phytophagous insect species.
What are the two major nutrients in plants? (2)
- Carbon (from Carbohydrates).
- Nitrogen (from Proteins).
Plant-Insect implications? (2)
- Elevated CO2 causes an increase in C & a decrease in N in plants. This is beneficial for plants but causes the dilution effect (increase in C:N ratio).
- Having less N means that insects are getting less nutrition, therefore elevated CO2 causes insects to have nutritional stress but they have strategies.
Strategies used by insects to combat nutritional stress caused by elevated CO2? (2)
- Compensatory feeding.
- Increasing midgut length.
Compensatory feeding?
= when insects increase their food intake to compensate for reduced nutrient quality in plants.
Types of insect herbivores? (5)
- Leaf chewers.
- Phloem feeders.
- Leaf miners.
- Root feeders.
- Gallers.
Leaf chewers & elevated CO2 attributes? (5)
- Most leaf-feeding species.
- Have chewy mouthparts.
- Feed on leaf tissue.
- Increased compensatory feeding but,
- Decreased development, size & fecundity.
Egs of leaf chewers? (3)
- Grasshoppers.
- Caterpillars.
- Locusts.
An exception to leaf chewers?
Locusts & elevated CO2.
Locusts & Elevated CO2 attributes? (3)
- Carbohydrate limited.
- Increased C:N ratios promote locust outbreaks (locust population booms).
- Locust population booms are a problem to agriculture, farmers.
Phloem feeders attributes? (5)
- Suck on sap.
- Most sap-sucking species.
- Mixed responses.
- Some are compensatory feeders.
- Certain aphid species benefit/thrive well as they benefit from high C content plants (extra sugars).
Eg of Phloem feeders?
Aphids.
Leaf miners attributes? (3)
- Eat the internal structure of leaves.
- Less well studied.
- Decreased development, size & fecundity (due to nutrient dilution in leaf tissue).
Eg of Leaf-mining insects?
Leaf miner moths.
Root feeders attributes? (3)
- Less well studied.
- Much less N in roots.
- Decreased development & survival (due to nutrient dilution in roots).
Eg of Root feeding insects?
Wireworms.
Gallers attributes? (3)
- Highly specialised to have a relationship with certain species.
- Less well studied.
- Variable responses.
Eg of Gallers?
Gall wasps.
How can an insect be more efficient at getting nitrogen from food?
Insects that feed on low nitrogen diets increase their midgut length in order to maximise nutrient absorption (gives food more time to digest/absorb).
Egs of insects that have increased their midgut length? (2)
- Lepidoptera (Caterpillars).
- Orthoptera (Grasshoppers).
Midgut changes in Lepidoptera (Caterpillars)? (2)
- Increased midgut length.
- Maximised absorption.
Midgut changes in Orthoptera (Grasshoppers)? (2)
- Increased midgut length & size.
- Maximised absorption.-
What’s the general trend with elevated CO2?
Decrease in insect size.
What happens when Carbon is added to plants (via elevated CO2)? (3)
- Dilution effect.
- Structural effect.
- Metabolite effect.
Dilution effect?
= where an increase in one component (carbon in plants) dilutes the concentration of another (nitrogen in plants), reducing the overall nutritional quality of plants.
Structural effect?
= where the increase in carbon in plants causes plants to be tougher to forage on.
Result of the Dilution effect & Structural effect?
Insects should now increase their feeding time & foraging time, which may result in trade-offs.
How do insects then adapt to the Structural effect?
Insects such as locusts change their foreguts by increasing their crop/gizzard size (to reduce the time spent eating more food). Therefore, they respond to more dignified grass.
Metabolite effect?
= where plants are increasing their phenolic compounds & tannins as CO2 levels increase.
Result of the Metabolite effect? (3)
- Plants are getting more defences.
- Plants are being less palatable.
- Intereferes with digestion of insect herbivores (makes plants harder to digest).
Eg of Metabolite effect in insects?
Seen in elevated CO2 & caterpillars, where the increased phenolic concentration in plants deters generalist insect herbivores.
Who can deal with increased plant defences better between specialists & generalists?
Specialists.
Why can specialists deal with increased plant defences better than generalists?
It’s because increased phenolic concentration benefits specialists, who have specialised digestive systems that make them more resilient.
Why can’t generalists deal with increased plant defences like specialists?
It’s because increased phenolic concentration causes decreased development, size & fecundity, making them more susceptible to plant defences.
Plant-Insect implications? (3)
- Dilution effect (High C:N ratios; Lower quality).
- Structural effect (Increased plant structure; Harder to eat).
- Metabolite effect (Increased metabolites; Harder to digest).
Way insect herbivores adapt to Dilution effect?
Compensatory feeding (generalists).
Way insect herbivores adapt to Structural effect?
Compensatory feeding (generalists).
Way insect herbivores adapt to Metabolite effect?
Feeding, but specific to specialists.
General implications of elevated CO2 on phytophagous insects? (4)
- Slowed growth due to increased C:N ratio.
- Prolonged development due to increased C:N ratio.
- Slow digestion due to increased C:N ratio & increased metabolites.
- Decreased fecundity/reproduction due to decreased body size & poor nutrition.
Super summary? (3)
- The basics (insects are poikilothermic; minimal direct effects; major indirect effects).
- Elevated CO2 & Insects (influence on plants; C:N ratios; structure; metabolites).
- General trends (elevated CO2; development; metabolism; reporduction).
